1. Field of the Invention
This invention relates to a key switch. More particular, the invention relates to a push button key switch suited for use as a data input key for a computer or word processor.
2. Description of the Prior Art
Many push button type key switches are used in the data input keyboards of computers, word processors and the like. Furthermore, as these electronic devices become more compact, there is increasing demand for the manufacture of thinner, more compact keyboards.
FIG. 3 illustrates a cross-sectional view of a key switch incorporated in a keyboard for a conventional compact electronic device.
In FIG. 3, numeral 1 denotes a keytop, on the upper face of which lettering has been printed or embossed. The keytop 1 is in the form of a cube, the underside of which is open, forming a cavity. A connector 3 is molded so as to protrude down from the middle of the inner cavity of the keytop 1. The connector 3 fits into a cylindrical key stem 5. A concave area 9 is formed inside the bottom end of the key stem 5, and a regulating ledge 7 is formed around its periphery. A frame 11 is disposed about the key stem 5. The frame 11 is molded together with the keyboard base 12 to form a single unit of synthetic resin. The portion formed around the key stem protrudes from the base and in cross-section has the from of a two-step plataform. The key stem 5 is guided on its periphery by a circular opening at the other end of the frame 11 such that the regulating ledge 7 at the bottom end of the key stem is brought into contact with the middle ledge of the frame 11. The concave area 9 of the key stem 5 fits over the head of a cup-shaped rubber spring 14 consisting of an elastic material such as rubber. The underside of the rubber spring 14 is in light contact with a backplate 16, which consists of a steel plate or other like hard, plate-like object. A laminar switch 18, which is in the form of a thin film, is formed on the surface of the backplate 16, i.e., on the portion with which the underside of the rubber spring 14 is in contact. The laminar switch 18 is constructed as follows; two pliable synthetic resin sheets, on the opposing faces of which electric contact points are provided, are placed facing each other with a small space between them in such a manner that the electric contact points are brought into contact as the synthetic resin sheets are pressed together by a protrusion 20 provided on the underside of the rubber spring 14. As such switches are already well known, a detailed explanation shall be omitted.
In the case of a conventional key switch with a construction such as that described, when the key top 1 is pressed down by the finger, the key stem 5, which is attached to the underside of the keytop 1, is guided by the round opening at the top of the frame 11 so that its bottom end depresses the rubber spring 14, causing it to collapse and the protrusion 20 inside it to press down on the laminar switch 18, thereby activating the key switch.
In the case of a key switch of this type, the rubber spring 14, the upper end of which is pressed down by the frame 11, is gradually deformed until it suddenly collapses at the time that a certain deformation threshold is exceeded. The operator experiences the impact at this time as a clicking sensation at the fingertips and gains a sense of how the key switch is operating. Though the more distinct the clicking sensation the better, obtaining such a distinct clicking sensation requires a design which provides a large keystroke distance for the rubber spring 14. This allows the distance through which the protrusion 20 on the rubber spring 14 moves, from its uppermost position to the point at which it activates the laminar switch 18, to be as great as possible. For this reason, the conventional key switch shown in FIG. 3 requires use of a key stem 5 which is long enough to allow use of a rubber spring 14 with a keystroke distance of some length. It is therefore also necessary for the height of the frame 11 which supports the key stem 5 to be correspondingly high.
With the rapid advances of portable computers, word processors and the like in recent years, there has been an attempt to make these devices thinner and more compact which has lead to a demand for thinner keyboards as well. Nevertheless, there is an even stronger demand, contradictory to the above, for use of a keyboard with favorable operating properties in which the long keystroke distance of conventional key switches for keyboards is maintained.